Spinoff technologies from space are another "sell the perception" thing. There's a lot of BS there. But as long as the public swallows it, it works to justify the program.
Even if you choose to ignore all that has come from it.. Space is quite possibly the most important thing we can be investing time, money and research into in terms of future advancement and sustainability of the human race.
Tell me: what exactly would have been worse if the US had never had a manned space program? The whole thing feels like a vanity project, not something that delivered value. It could all have been delayed while launchers got cheaper without loss, as far as I can tell.
Kapton is a great example of the spinoff racket. You take something that was USED in the space program (but not invented by NASA; Kapton came from Dupont), you carefully blur the story, and now you claim it was the RESULT of the space program. It doesn't help that the marketing of these things often used the space program, calling them "Space Age", trying to mooch off the glamour Apollo had at the time. Integrated circuits, teflon, velcro, glass ceramics are other examples.
Moonshot programs are what create demand for the sort of R&D that Dupont did to bring kapton to market.
Polyimides date back to 1902, but you couldn't buy anything like kapton tape before the space programs created a need for such materials and capital to build out plant for them.
I promise you there was enormous demand for products to stimulate R&D outside of NASA. Orders of magnitude more. That's why technology was leaping ahead even before NASA existed, and even after NASA's budget shrank. It's also why all that new technology came out of countries without manned space programs.
To make a valid spinoff argument, you have to show that the particular technology would not have come about without NASA. That sort of contrafactual, alt-history argument is really hard to do. It's why alt history has such a bad name in history circles -- you can't really show anything. This means all spinoff claims are dubious. Not only are they presented without the necessary evidence, it's difficult to see how the evidence ever could be acquired.